Transcutaneous CO2 Monitoring as Indication for Inpatient NIV Initiation in Patients with ALS

Amyotrophic lateral sclerosis (ALS) is characterized by profound muscle weakness, including diaphragmatic weakness resulting in hypercapnic respiratory failure. While non-invasive ventilation (NIV) is usually initiated in the home, patients presenting with hypercapnic respiratory failure may be at high risk of adverse outcomes with delays in treatment. We aim to describe the clinical utility of transcutaneous CO2 (TCO2 ) to assess the need for inpatient initiation of NIV.Eight patients from the University of Michigan Pranger ALS clinic were directly admitted to the hospital for urgent initiation of NIV between May 2020-May 2021. A retrospective review of electronic medical records, including pre-hospital pulmonary function assessments, hospitalization blood gases, and NIV use metrics was performed.All eight patients had symptoms of respiratory insufficiency at time of admission, although not all patients had forced vital capacity (FVC) measurements that would identify need for NIV. All patients had measured TCO2 > 45 mmHg. Seven of eight patients had worsening hypercapnia after admission, indicating advanced respiratory failure. All patients were titrated to tolerance of continuous nocturnal NIV while in the hospital, with an average length of stay of 6.5 days (range, 3-8). All patients demonstrated compliance with NIV, >4 h, at post-hospital follow-up.Many current ambulatory measurements underestimate, or incompletely evaluate, respiratory dysfunction, and arterial blood gases are not typically readily available. Outpatient TCO2 measurements can serve as a useful screening tool to identify ALS patients who would benefit from inpatient initiation and titration of NIV.